To start with, measure the p-rods that are in it now to be sure they're not shorter than stock.
You say you know how to adjust valves. This may be true but bear w/me for a moment.
When you are twisting the p-rod to determine that the lash has been removed, and can begin to turn down the adjusting nut to get the proper preload, the "oily pushrod no longer rotates easily by fingers" part is what I'm questioning.
There should be no point when "zero" lash has been met that the p-rod should no longer rotate easily- it sounds like you're too far and have bottomed out the plunger in the lifter body and are now against the valve spring pressure.
When at "Zero" lash, the p-rod will still rotate very easily, there's only a very slight amount of drag that is created when the p-rod and lifter plunger/seat have met.
Bottom line- adjust the valves correctly and there will be no bottoming out of the rocker on the stud boss. Just be glad that you didn't bend any valves or p-rods by trying to run the engine like this.
You may need a slightly different length of p-rod to adjust the geometry to perfection, but stock length will work to get the valves adjusted to check it if you don't have a tool to check p-rod legnth.